1. Technical Background of the Invention
The invention relates to a device for constraining a wheel and tire assembly on a platform.
Specifically, though not exclusively, the device can be applied on machines for mounting and dismounting tires on wheels which machines have a self-centered platform, which is equipped with means for gripping and centering the wheel and which is rotatable about a normally vertical axis.
2. Prior Art
In tire changing machines there is always the prime need to protect the operator against any tire explosion during the inflating operation, which is usually done with the tire mounted on the platform. Without appropriate safety systems keeping the wheel in its position on the platform any explosion would have disastrous effects. The wheel would be projected violently away from the platform, causing great risk to the operator and to anyone else who found themselves in the vicinity of the machine.
Known safety systems comprise a horizontal arm, situated above the platform and rotatable on command about a vertical rotation axis, to which it is slidably coupled, with a vertical axis, a stem bearing at an extremity thereof a plate that can be positioned in contact with a wheel placed (centered and blocked) on the platform. Before inflating the tire, the operator secures the wheel to the platform by positioning the rotatable arm on the platform and setting the plate above the central part of the wheel rim, thus exploiting the arm's ability to slide vertically. Then, using a locking device generally cam-activated, he constrains the stem to the arm so that the wheel is solidly anchored on the platform so as to be constrained thereon even when subjected to very violent solicitation, as in the case of an explosion.
In known devices, usually the stem is immobilized to the arm by means of a manually-actuable clamp mounted on the arm and comprising a rotatable cam-type control lever. This clamp, however is not secure and reliable enough, especially as the cam is subject to wear which might, after many anchoring and unblocking operations lead to a deterioration in blocking effectiveness.